1. Field of the Invention
The present invention relates generally to rod guides for use in hydrocarbon producing wells and, more particularly, to a plastic rod guide having an improved slot therein for a facilitating installation of the rod guide onto a sucker rod.
2. Description of the Background
Rod guides have been used for years to minimize wear on both sucker rod strings and on tubular strings. Sucker rod strings are typically provided within a tubular string to operate a downhole pump that is designed to pump production fluid upwardly through the annulus between the tubular string and the sucker rod string. Rod guides are typically utilized to centralize and guide the sucker rod string within the tubular string and thereby prevent wear caused by metal-to-metal scraping between the sucker rod and the tubular string. Rod guides may also serve as scrappers to clean paraffin or other material off the inside of the tubular string. A plurality of rod guides are preferably axially spaced at regular intervals along the sucker rod string of a well using a downhole pump to recover oil. The pump may be powered by either rotation or reciprocation of the sucker rod string.
One type of rod guide includes a generally cylindrical-shaped, longitudinally slotted guide body with a longitudinal internal bore that is preferably slightly undersized with respect to the diameter of the sucker rod on which the rod guide is installed. An expandable body slot extends longitudinally through the entire length of the rod guide and provides a means for securely mounting the rod guide at a desired location on the sucker rod. The rod guide may be affixed to the sucker rod by initially placing the rod guide against the sucker rod with the mouth or entry port of the expandable body slot lying adjacent and in line with the sucker rod. The rod guide is then struck sharply with a hammer or mallet to momentarily spring the body slot open and force the rod guide onto the sucker rod. The sucker rod will then seat securely in the preferably slightly undersized internal bore of the rod guide. The rod guide preferably is secured to the sucker rod so that the rod guide stays in position on the rod over the extended life of the rod guide as the sucker rod is reciprocated or rotated within the tubular string. For this reason, the configuration of the rod guide body and the material for the rod guide may be designed to provide a strong biasing action to securely grip the sucker rod, as disclosed in U.S. Pat. No. 4,858,688.
Problems sometimes occur during installation of the rod guide onto the sucker rod due to this desired strong biasing action. Often, many mallet blows are necessary to install the rod guide onto the sucker rod, thereby increasing installation time. These repeated mallet blows may also damage the rod guide. Sometimes, during or after the first blow, the rod guide may pop back off the sucker rod towards the operating personnel.
Various designs for a slot in a rod guide have been provided. Slots have been used that have a slot cross-section, with respect a horizontal plane perpendicular to the internal bore of the guide, that has straight substantially parallel slot walls. As well, rod guide slots have been designed that have planar slot walls that are tapered. In one tapered slot design, the mouth or entry port into the slot is wide and tapers through the throat of the slot to a smaller width at the exit port of the slot (which opens to the internal bore of the rod guide). Another design has a relatively small mouth or entry port that tapers through the throat of the slot to a somewhat wider slot exit port. Examples of these rod guides are disclosed in U.S. Pat. Nos. 4,938,285 and 5,154,867. Some knock-on rod guides include circumferentially spaced slots to form vanes which help clear paraffin off the tubing.
The slot designs for these rod guides affect the likelihood that the rod guide will pop back at the operating personnel, but do not alleviate this concern. Many blows to the rod guide may still be required to effect installation. Some rod guide designs sacrifice long life of the rod guide by selecting a plastic material which is less durable when exposed to abrasive wellbore conditions, but may be reliably secured to a rod. Other designs utilize a durable plastic material, but the installed rod guide is susceptible to movement with respect to the rod after extended downhole use.
Consequently, there remains a need for a more dependable, less time consuming method for installing rod guides onto sucker rods to reduce costs and to decrease the likelihood of injury associated with such installation. A rod guide which may be more reliably installed and which will remain secured to a rod has a significant advantage over other rod guides. According to this invention, the configuration of the rod guide and the material selection for the guide body may be optimized with less regard to installation difficulty. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.